OBJECTIVES: The overall long-range objectives of the proposed research are to determine whether ionizing and nonionizing radiations interact in the induction of mutation and neoplastic transformation, to identify the nature of the interaction, and to establish the possible relationship between the repair processes and the expression of interactive damage related to mutation and neoplastic transformation. The primary objectives for the current year were to develop methodology and to determine the appropriate conditions for the measurement of the induction of 6-thioguanine (6-TG) and ouabain (OUA) resistant cells by various irradiations. Based upon the mutation expression times required for the different radiation induction curves were to be obtained. Preliminary measurements of the incidences of neoplastic transformation by nonionizing radiations were to be extended. Research will be continued by determining: 1) the dose dependencies for X-rays plus nonionizing radiation using the 6-TG marker: 2) the effect of dose fractionation on mutation induction with single and mixed radiations will be measured: 3) attempts will be made to determine the age dependence of 6-TG- and/or OUA-induced resistance; and 4) measurements will be initiated of the induction of neoplastic transformation by combinations of ionizing and nonionizing radiations.